Energy consumption meters are used for detecting consumed or generated electrical energy. Such energy consumption meters are also referred to as electricity meters or kilowatt hour meters.
In the case of electronically operating energy consumption meters, voltage and current are normally detected, digitized and multiplied by one another. After the multiplication, the instantaneous electrical power is provided. If this electrical power is integrated or accumulated over time, a signal is obtained which is a measure of the electrical energy generated or consumed in a specific period of time.
In order to obtain signals which are proportional to electrical voltage and to electrical current, voltage dividers, voltage transformers, current transformers or other means for coupling out signals can be used.
In many applications it is necessary to provide DC isolation at least in one of the two channels for detecting voltage and current. Such a DC isolation of the circuits is provided by a transformer, for example.
One problem with such transformers, however, is the phase shift caused by the inductive coupling of the transformer. The phase shift results firstly between the output signal and the input signal of the transformer. Secondly, the phase shift also results between the signal representing the current and that representing the voltage, however.
This results in undesirable measurement errors during the multiplication of voltage and current, however. In this case it is necessary to take care that the voltage and current are generally not present in the form of DC signals, but rather in the form of AC signals having a more or less harmonic signal shape.
The described problem is further intensified, in addition, by the fact that, even when in each case one transformer-based transfer arrangement is inserted in the voltage and current measurement channel, an unpredictable phase shift between the two input channels may be caused by manufacturing tolerances, thermal effects, ageing effects etc.
In order to correct the undesirable phase shift described, for example RC networks which comprise resistors and capacitors could be used. However, these RC networks normally need to be in the form of additional external components and, disadvantageously, cannot normally be integrated. In addition, the problem of manufacturing-related and temperature-related tolerances is in principle not solved by this means.